"Gen. Shinseki has served our country with distinction. I now believe he should step aside in order to allow our focus and our efforts to be on making the critically needed changes to fix the VA," Warner said in a statement.

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"The controversy over Gen. Shinseki's leadership has taken attention away from the real issue — the need for swift, decisive action to reform the VA, change its culture, and ensure that we provide quality, timely services for our veterans," Warner said.

Warner joins five other Democratic senators in calling for Shinseki's ouster: Sens. Al Franken (Minn.), Kay Hagan (N.C.), Jeanne Shaheen (N.H.), Mark Udall (Colo.) and John Walsh (Mont.). All of the senators are up for reelection this fall, with Warner facing a competitive challenge from former Republican National Committee Chairman Ed Gillespie.

Calls for Shinseki's resignation are mounting after the VA's inspector general released a damaging interim report on Wednesday that substantiated claims that staff at a Phoenix clinic concealed long wait times for appointments.

The conservative Concerned Veterans of America launched an ad campaign Wednesday aimed at Warner and four other Democratic senators facing reelection over the VA scandal. The campaign is meant to pressure the lawmakers into backing a bill that would allow the VA secretary more leeway to fire employees.

Warner sought to burnish his credentials on VA accountability in his statement, saying, "No one has pushed the VA harder than me."

He cited pressuring the department to broaden services for female veterans with post-traumatic stress disorder, to reduce the claims backlog, and to provide veterans with help on filing tough claims.

“It is important that we provide Virginia's veterans with the services they have earned — and which we as a nation have committed to provide,” he said.

“Like most Americans, I am outraged about how our veterans are being treated. The preliminary Inspector General’s report shows this is a systemic problem that dates back many years. We have to fix the system now," he said.